Helical tomotherapy (1.) is a new IMRT technology for radiation treatment of cancer, invented here at the University of Wisconsin - Madison, and is in the initial stages of operation at the University of Wisconsin Comprehensive Cancer Center. It is the marriage of a linac with a CT scanner. The delivered dose uniformity is potentially compromised in helical tomotherapy by unique delivery "artifacts" that arise from inherent geometrical constraints in the device as well as target motion common to all IMRT technologies. The proposed work involves the exploration of the thread artifact arising from the small cone-angle of the Fan-beam, the discrete delivery artifact arising from the phasing of the 51 delivery angles, and a motion artifact, similar to other IMRT technologies, but with different parameters in current tomotherapy device. The candidate, Dr. Michael Kissick, is an established scientist in plasma physics and nuclear fusion, but has recently switched fields into medical physics, bringing a great deal of physical science research and analytical skills to the medical field. The goal of the project is to develop viable solutions to these artifacts, while small for most situations, can be larger for some challenging cases such as large field plans that would require a high pitch delivery. Such solutions would extend the applicability of tomotherapy in its clinical use in cancer treatment. 1. "Helical Tomotherapy," T.R. Mackie, et al., Intensity Modulated Radiation Therapy - The State of the Art, ed. J.R. Palta and T.R. Mackie, Proceedings of the American Association of Physicists in Medicine (AAPM) 2003 Summer School Proceedings, Colorado Springs, CO, June 22-26, 2003, page 247, Medical Physics Monograph No. 29, Medical Physics Publishing, Madison, Wl.